+ Location

• Spinal cord tumors are classified as extradural, intradural-extramedullary, or intramedullary
• Extradural tumors are most common and account for 50% of spinal tumors
• Intradural-extramedullary account for 30% and intramedullary account for 15% of spinal tumors

+ Signalment

• 90% of spinal tumors occur in large breed dogs
• 28% of spinal tumors occur in cats and dogs < 3 years

+ General Considerations

• Spinal cord tumors are uncommon in dogs
• Meningioma is the most common with a predilection for the cervical spinal cord
• Other primary tumors include LSA, MCT, and intradural-extramedullary spinal cord tumor of young dogs
• HSA is the most common metastatic tumor, but others include pilomatrixoma and pheochromocytoma

+ Extradural Spinal Cord Tumors

• Primary vertebral tumors and multiple myeloma
• Other extradural tumors include myxoma, myxosarcoma, LSA, and lipoma or liposarcoma

+ Intradural-Extramedullary Spinal Cord Tumors

• Meningioma and peripheral nerve sheath tumors are the most common intradural-extramedullary tumors
• Spinal meningioma accounts for 14% of all CNS meningioma
• Spinal meningioma has a predilection for the cervical spinal cord:
• 40%-77% cervical spinal cord
• 0%-32% thoracic spinal cord
• 23%-28% lumbar spinal cord
• Peripheral nerve sheath tumors involve the spinal cord in 65% cases
• Other intradural-extramedullary tumors include hemangioma (common), myxoma, myxosarcoma, and an unusual case of diffuse meningeal tumor affecting entire meningeal surface of CNS

+ Intradural-Extramedullary Spinal Cord Tumor of Young Dogs

• Uncommon
• Synonyms: ependymoma, neuroepithelioma, spinal cord blastoma, medulloepithelioma, hamartoma, and nephroblastoma
• Age: 6 months to 3 years
• Breed predisposition: GSD, Labrador Retriever, and Golden Retriever
• Clinical signs: lateralized with vast majority of lesions between T10-L2
• Microscopically similar to nephroblastoma and some believe this tumor may represent extrarenal nephroblastoma arising from ectopic mesonephric or metanephric tissue trapped within the dura during embryologic development
• Diagnosis: CSF findings are usually non-specific, but albuminocytologic dissociation may be consistent with a chronic neoplastic process
• Treatment: cytologic reduction or removal associated with long-term survival (4 months and > 3 years) ± radiation therapy for incompletely excised tumors

+ Intramedullary Spinal Cord Tumors

• Intramedullary spinal cord tumors are uncommon
• Intramedullary spinal cord tumors usually have glial cell origin: astrocytoma, oligodendroglioma, undifferentiated sarcoma, ependymoma, and choroid plexus papilloma
• Intramedullary spinal cord tumors are most commonly located between C6-T2
• Intramedullary spinal cord metastasis can also occur before evidence of the primary tumor
• Primary tumors with a propensity for metastasizing to the spinal cord include HSA and LSA ± mammary ADC and malignant melanoma
• Malformation tumors may also affect the spinal cord parenchyma such as epidermoid cyst and hamartoma

+ History

• Extradural spinal cord tumors are usually slow growing and progressive over weeks to months
• Acute onset of neurologic signs may be caused by tumor-induced hemorrhage or ischemia
• Intramedullary tumors have a more rapid growth rate and have a higher incidence of hemorrhage, ischemia, and necrosis

+ Clinical Signs

• Clinical signs depend on the tumor location and are difficult to differentiate from other causes of myelopathy
• Extradural tumors may involve the meninges, spinal nerves, or nerve roots which results in varying levels of pain from discomfort to extreme spinal hyperesthesia
• Tumors involving the brachial or lumbar intumescence may cause lameness, limb elevation, neurogenic muscle atrophy, and depressed spinal reflexes
• Hyperesthesia is associated with extradural and intradural-extramedullary tumors, but not intramedullary tumors
• Fundus, lymph node, and rectal examination should be performed for evidence of LSA or metastatic lymphadenopathy

+ Survey Radiographs

• Thoracic radiographs for evaluation of metastatic disease
• Radiographic findings include cortical lysis with collapse of the adjacent intervertebral disk space
• Vertebral body and dorsal lamina are more frequently affected than dorsal and transverse spinous processes
• Radiographic signs not always visible due to inconsistent vertebral shape, overlying ribs and soft tissue, and improper positioning
• Cortical bone destruction is a late event in metastatic vertebral lesions
• Radiographic abnormalities associated with non-vertebral spinal cord tumors are rare, but slow and progressive tumor growth may cause enlargement of an intervertebral foramen or vertebral canal with thinning of cortical bone

From: Withrow SJ & MacEwen EG (eds): Small Animal Clinical Oncology (3rd ed).

+ Cerebrospinal Fluid Analysis

• CSF collection and analysis are recommended if survey radiographs are inconclusive
• CSF is collected from a lumbar site and needle left in situ for myelography
• CSF changes include increased protein content and normal to increased white cell count
• CSF findings with LSA include increase white cell count with abnormal lymphocytes
• Abnormal CSF findings are more common in dogs with spinal LSA due to leptomeningeal involvement

+ Myelography

• Indications: determining presence, anatomical location and dural site of spinal cord tumor
• Spinal cord tumors are classified as extradural, intradural-extramedullary, or intramedullary
• Classification may be difficult due to spinal cord edema

From: Withrow SJ & MacEwen EG (eds): Small Animal Clinical Oncology (3rd ed).

+ Advanced Imaging

• CT is recommended for vertebral tumors due to excellent bone detail
• However, myelography is superior to CT in differentiating intramedullary from intradural-extramedullary
• MRI is recommended for spinal cord tumors due to excellent soft tissue detail
• MRI provides accurate information on anatomic location and bone involvement, but differentiation between intradural, extradural and intramedullary, and extramedullary difficult

+ General Considerations

• Management options depends on tumor location, extent, and histologic type
• Aim: alleviate spinal cord compression
• Treatment options include conservative (with corticosteroids) and surgery
• Surgery allows decompression ± complete removal or cytoreduction of the mass
• Surgical decompression techniques include hemilaminectomy and dorsal laminectomy
• Complete resection of spinal meningioma is complicated by adhesions to the pia mater or spinal cord, and friable texture resulting in piecemeal dissection
• Rhizotomy can be performed to facilitate tumor resection, but avoided in the brachial and lumbar intumescence
• Radiation therapy can be used for LSA, incompletely resected spinal tumors, and when surgery is not feasible
• Spinal cord is resistant to the acute effects of radiation due to low replication rate, but late effects (> 2 years) can be seen due to progressive demyelination and malacia of white matter (especially oligodendrocytes, endothelial cells, astrocytes, and microglial cells)

+ General Considerations

• Prognosis depends on resectability, histologic type, location, and severity of neurologic signs
• Poor prognosis for metastatic and vertebral tumors

+ Surgery

• Guarded to good prognosis for intradural-extramedullary lesions following surgical resection
• Overall MST 240 days for surgically resected spinal cord tumors:
• MST 180 days for malignant spinal tumors
• MST 1,410 days for benign spinal tumors
• 56% dogs with spinal meningioma alive > 6 months
• Poor prognostic factors for spinal meningioma include tumors located in either the cervical or lumbar intumescence, ventral tumors, and iatrogenic cord trauma during dissection

+ Radiation Therapy

• Guarded to good prognosis for intramedullary tumors treated with radiation therapy with normal spinal cord tolerating radiation well and neurologic signs alleviated > 1 year
• MST 17 month MST for intradural-extramedullary and intramedullary tumors following cytoreductive surgery and radiation therapy